2-hydroxybenzophenone UV dyes for laser recording process

ABSTRACT

A laser recording element comprising a support having thereon a dye layer comprising an image dye dispersed in a polymeric binder, said dye layer having an infrared-absorbing material associated therewith, and wherein said dye layer also contains a 2-hydroxybenzophenone UV-absorbing dye.

This invention relates to use of 2-hydroxybenzophenone UV dyes in asingle-sheet laser recording element.

In recent years, thermal transfer systems have been developed to obtainprints from pictures which have been generated electronically from acolor video camera. According to one way of obtaining such prints, anelectronic picture is first subjected to color separation by colorfilters. The respective color-separated images are then converted intoelectrical signals. These signals are then operated to produce cyan,magenta and yellow electrical signals. These signals are thentransmitted to a thermal printer. To obtain the print, a cyan, magentayellow dye-donor element is placed face-to-face with a dye-receivingelement. The two are then inserted between a thermal printing head and aplaten roller. A line-type thermal printing head is used to apply heatfrom the back of the dye-donor sheet. The thermal printing head has manyheating elements and is heated up sequentially in response to the cyan,magenta and yellow signals. The process is then repeated for the othertwo colors. A color hard copy is thus obtained which corresponds to theoriginal picture viewed on a screen. Further details of this process andapparatus for carrying it out are contained Pat. No. 4, 621, 271, thedisclosure of which is hereby incorporated by reference.

Another way to thermally obtain a print using the electronic signalsdescribed above is to use a laser instead of a thermal printing head. Insuch a laser transfer system, the donor sheet includes a material whichstrongly absorbs at the wavelength of the laser. When the donor isirradiated, this absorbing material converts light energy to thermalenergy and transfers the heat to the dye in the immediate vicinity,thereby heating the dye to its vaporization temperature for transfer toa receiver. The absorbing material may be present in a layer beneath thedye and/or it may be admixed with the dye. The laser beam is modulatedby electronic signals which are representative of the shape and color ofthe original image, so that each dye is heated to cause volatilizationonly in those areas in which its presence is required on the receiver toreconstruct the color of the original object. Further details of thisprocess are found in GB 2,083,726A, the disclosure of which is herebyincorporated by reference.

In another mode of imaging using a laser beam, a laser recording elementwith a dye layer composition comprising an image dye, aninfrared-absorbing material, and a binder coated onto a substrate isimaged from the dye side. The energy provided by the laser drives offthe image dye and other components of the dye layer at the spot wherethe laser beam impinges upon the element. In "laser removal" imaging,the laser radiation causes rapid local changes in the imaging layer,thereby causing the material to be removed from the layer. Usefulness ofsuch a laser recording element is largely determined by the efficiencyat which the imaging dye can be removed on laser exposure. Thetransmission Dmin value is a quantitative measure of dye clean-out: thelower its value at the recording spot, the more complete is the attaineddye removal.

In U.S. Ser. No. 259,588 of DoMinh et al., filed Jun. 14, 1994, asingle-sheet laser recording element is described which employs acertain liquid UV-absorbing dye. However, there is a problem with thisUV-absorbing dye in that under accelerated light fade conditions, theloss in UV density is pronounced, as will be shown by comparative testshereafter.

U.S. Pat. 5,256,506, in column 12, describes various non-black bodyabsorbers such as dicinnamalacetone and benzophenone derivatives whichare supposed to be useful in graphic arts masks. However, there is aproblem with dicinnamalacetone in that under accelerated light fadeconditions, the loss in UV density is pronounced, as will be shown bycomparative tests hereafter. There also is a problem with benzophenonein that it has insufficient UV absorption to be an effective graphicarts mask, as will be shown by comparative tests hereafter.

It is an object of this invention to provide a UV-absorbing dye whichwill have both an acceptable level of UV absorption and improvedstability to UV density loss from light exposure. It is another objectof this invention to provide a single-sheet process which does notrequire a separate receiving element.

These and other objects are achieved in accordance with the inventionwhich comprises a laser recording element comprising a support havingthereon a dye layer comprising an image dye dispersed in a polymericbinder, the dye layer having an infrared-absorbing material associatedtherewith, and wherein the image dye is a 2-hydroxybenzophenoneUV-absorbing dye.

In a preferred embodiment of the invention, the 2-hydroxybenzophenoneUV-absorbing dye has the following structure: ##STR1## wherein: R¹ andR² each independently represents hydroxy, alkyl, aryl, fused aryl, fusedheteroaryl, carboxy, alkylcarbonyl, arylcarbonyl, hydrogen, alkenyl,cycloalkyl, haloalkyl, cyanoalkyl, hydroxyalkyl, alkoxy, alkoxyalkyl,aryloxyalkyl, alkoxyalkylcarbonyl, aryloxyalkylcarbonyl,alkoxy-alkoxyalkyl, hydroxyalkoxyalkyl, tetrahydrofurfuryl,alkenyloxyalkyl, alkoxycarbonyloxyalkyl, alkenylcarbonyl,aryloxyalkylcarbonyl, aminoalkyl, cyanoalkylcarbonyl, haloalkylcarbonyl,alkylamino, arylamino, amino or halogen;

m is an integer of 1 to 4; and

n is an integer of 1 to 5.

The 2-hydroxybenzophenone UV-absorbing dye may be used in an amount offrom about 0.05 to about 1.0 g/m² of element.

In a preferred embodiment of the invention, in the above formula, m andn are each 1, R¹ is CH₃, OCH₃ or Cl and R² is OH or H.

Specific examples of UV dyes according to the above formula include thefollowing:

    ______________________________________                                         ##STR2##                                                                     Com-                                                                          pound R.sup.1          m     R.sup.2     n                                    ______________________________________                                        A     5-CH.sub.3       1     2-OH        1                                    B     5-OCH.sub.3      1     H           1                                    C     5-Cl             1     H           1                                    D     4-OH             1     3-Cl        1                                    E     5-C.sub.2 H.sub.5                                                                              1     3-CH.sub.3  1                                    F     6-COCH.sub.3     1     2-Cl, 6-Cl  2                                    G     H                1     4-CH.sub.2 CH.sub.2 OCH.sub.3                                                             1                                    H     5-C.sub.4 H.sub.9 -t                                                                           1     3-CH.sub.2 OC.sub.6 H.sub.5                                                               1                                    I     4-CH.sub.2 OCH.sub.2 OCH.sub.3                                                                 1     5-N(CH.sub.3).sub.2                                                                       1                                    J     6-CH.sub.3, 4-CH.sub.3                                                                         2     2-OH, 4-CH.sub.3                                                                          2                                    K     5-CH.sub.2 OCHCHCH.sub.3                                                                       1     4-CH.sub.2 CH.sub.2 CH.sub.2 CN                                                           1                                    L     3-CH.sub.3, 4-COCHCH.sub.2                                                                     2     H           1                                    M     4-CH.sub.3, 5-CH.sub.2 CH.sub.3                                                                2     3-COC.sub.6 H.sub.5                                                                       1                                    N     4-CHCHCH.sub.3   1     2-Cl, 4-Cl, 6-Cl                                                                          3                                    ______________________________________                                    

A visible image dye can also be used in the laser recording elementemployed in the invention provided it can be removed by the action ofthe laser. Especially good results have been obtained with dyes such asanthraquinone dyes, e.g., Sumikaron Violet RS® (product of SumitomoChemical Co., Ltd.), Dianix Fast Violet 3R-FS® (product of MitsubishiChemical Industries, Ltd.), and Kayalon Polyol Brilliant Blue N-BGM® andKST Black 146® (products of Nippon Kayaku Co., Ltd.); azo dyes such asKayalon Polyol Brilliant Blue BM®, Kayalon Polyol Dark Blue 2BM®,(products of Nippon Kayaku Co., Ltd.); direct dyes such as Direct DarkGreen B® (product of Mitsubishi Chemical Industries, Ltd.) and DirectBrown M® (product of Nippon Kayaku Co. Ltd.); acid dyes such as KayanolMilling Cyanine 5R® (product of Nippon Kayaku Co. Ltd.); basic dyes suchas Sumiacryl Blue 6G® (product of Sumitomo Chemical Co., Ltd.), andAizen Malachite reen® (product of Hodogaya Chemical Co., Ltd.); ##STR3##or any of the dyes disclosed in U.S. Patents 4,541,830, 4,698,651,4,695,287, 4,701,439, 4,757,046, 4,743,582, 4,769,360, and 4,753,922,the disclosures of which are hereby incorporated by reference. The abovedyes may be employed singly or in combination. The dyes may be used at acoverage of from about 0.05 to about 1 g/m² and are preferablyhydrophobic.

Another embodiment of the invention relates to a process of forming adye image comprising imagewise-heating, by means of a laser, therecording element described above, the laser exposure taking placethrough the dye side of the element and causing dye to be removedimagewise to obtain the dye image in the recording element.

The laser recording elements of this invention can be used to obtainmedical images, reprographic masks, printing masks, etc. The imageobtained can be a positive or a negative image. The dye removal processcan generate either continuous (photographic-like) or halftone images.

The invention is especially useful in making reprographic masks whichare used in publishing and in the generation of printed circuit boards.The masks are placed over a photosensitive material, such as a printingplate, and exposed to a light source. The photosensitive materialusually is activated only by certain wavelengths. For example, thephotosensitive material can be a polymer which is crosslinked orhardened upon exposure to ultraviolet or blue light but is not affectedby red or green light. For these photosensitive materials, the mask,which is used to block light during exposure, must absorb allwavelengths which activate the photosensitive material in the Dmaxregions and absorb little in the Dmin regions. For printing plates, itis therefore important that the mask have high blue and UV Dmax. If itdoes not do this, the printing plate would not be developable to giveregions which take up ink and regions which do not.

By use of this invention, a mask can be obtained which has enhancedlight stability for making multiple printing plates or circuit boardswithout mask degradation.

Any polymeric material may be used as the binder in the recordingelement employed in the invention. For example, there may be usedcellulosic derivatives, e.g., cellulose nitrate, cellulose acetatehydrogen phthalate, cellulose acetate, cellulose acetate propionate,cellulose acetate butyrate, cellulose triacetate, a hydroxypropylcellulose ether, an ethyl cellulose ether, etc., polycarbonates;polyurethanes; polyesters; poly(vinyl acetate); polystyrene; poly(styrene-co-acrylonitrile); a polysulfone; a poly (phenylene oxide); apoly (ethylene oxide); a poly(vinyl alcohol-co-acetal) such aspoly(vinyl acetal), poly(vinyl alcohol-co-butyral) or poly(vinylbenzal); or mixtures or copolymers thereof. The binder may be used at acoverage of from about 0.1 to about 5 g/m².

In a preferred embodiment, the polymeric binder used in the recordingelement employed in the process of the invention has a polystyreneequivalent molecular weight of at least 100,000 as measured by sizeexclusion chromatography, as described in U.S. Pat. No. 5,330,876, thedisclosure of which is hereby incorporated by reference.

A barrier layer may be employed in the laser recording element of theinvention if desired, as described in copending U.S. Ser. No. 321,282,filed Oct. 11, 1994, and entitled BARRIER LAYER FOR LASER ABLATIVEIMAGING, now U.S. Pat. No. 5,459,017, the disclosure of which is herebyincorporated by reference.

To obtain a laser-induced image according to the invention, an infrareddiode laser is preferably employed since it offers substantialadvantages in terms of its small size, low cost, stability, reliability,ruggedness, and ease of modulation. In practice, before an infraredlaser can be used to heat a recording element, the element must containan infrared-absorbing material, such as cyanine infrared-absorbing dyesas described in U.S. Ser. No. 099,969, filed Jul. 30, 1993, andentitled, "INFRARED-ABSORBING CYANINE DYES FOR LASER ABLATIVE IMAGING",now abandoned or other materials as described in the following U.S. Pat.Nos.: 4,948,777, 4,950,640, 4,950,639, 4,948,776, 4,948,778, 4,942,141,4,952,552, 5,036,040, and 4,912,083, the disclosures of which are herebyincorporated by reference. The laser radiation is then absorbed into thedye layer and converted to heat by a molecular process known as internalconversion. Thus, the construction of a useful dye layer will depend notonly on the hue, transferability and intensity of the image dyes, butalso on the ability of the dye layer to absorb the radiation and convertit to heat. The infrared-absorbing dye may be contained in the dye layeritself or in a separate layer associated therewith, i.e., above or belowthe dye layer. Preferably, the laser exposure in the process of theinvention takes place through the dye side of the recording element,which enables this process to be a single-sheet process, i.e., aseparate receiving element is not required.

Lasers which can be used in the invention are available commercially.There can be employed, for example, Laser Model SDL-2420-H2 from SpectraDiode Labs, or Laser Model SLD 304 V/W from Sony Corp.

The dye layer of the laser recording element of the invention may becoated on the support or printed thereon by a printing technique such asa gravure process.

Any material can be used as the support for the recording element of theinvention provided it is dimensionally stable and can withstand the heatof the laser. Such materials include polyesters such as poly(ethylenenaphthalate); polysulfones; poly(ethylene terephthalate); polyamides;polycarbonates; cellulose esters such as cellulose acetate; fluorinepolymers such as poly(vinylidene fluoride) orpoly(tetrafluoroethylene-co-hexa-fluoro propylene); polyethers such aspolyoxymethylene; polyacetals; polyolefins such as polystyrene,polyethylene, polypropylene or methylpentene polymers; and polyimidessuch as polyimide-amides and polyether-imides. The support generally hasa thickness of from about 5 to about 200 μm. In a preferred embodiment,the support is transparent.

The following example is provided to illustrate the invention.

EXAMPLE

The following materials were employed in this example: ##STR4##

A 100 μm thick poly(ethylene terephthalate) support was coated with adye layer consisting of 0.22 g/m² infrared dye IR-1, 0.60 g/m²nitrocellulose, and either 0.27 g/m² of Control-1 or 0.86 mmol/m² ofControl-2, Control-3, Compound A, Compound B or Compound C coated fromtetrahydrofuran.

The stability of the resulting dye layers was measured using an X-RiteDensitometer (Model 361T, X-Rite Corp.) by the percent change in UVdensity between a covered and uncovered sample after exposure to fourhours of 50 kLux sunshine. The following results were obtained:

    ______________________________________                                               Target    UV         UV        Percent                                        Laydown   Density    Density   UV                                      Dye    (g/m.sup.2)                                                                             COVERED    UNCOVERED Change                                  ______________________________________                                        A      0.21      1.24       1.09      -12                                     B      0.20      0.71       0.63      -11                                     C      0.20      0.86       0.81       -6                                     Control-1                                                                            0.27      2.98       2.13      -29                                     Control-2                                                                            0.25      2.16       0.18      -92                                     Control-3                                                                            0.16      0.20       0.23      +11                                     ______________________________________                                    

The above results show that the dyes of the invention have a substantialimprovement in UV density loss, and thus are more resistant to fading inthe UV than Control dyes 1 and 2. Control dye 3 has insufficient UVdensity to be an effective graphic arts mask material.

Printing

Samples of the above example were laser written on a drum printer usinga laser diode print head, where each laser beam has a wavelength rangeof 830-840 nm and a nominal power output of 550 mW at the film plane.

The drum, 53 cm in circumference, was rotated at varying speeds and theimaging electronics were activated to provide adequate exposure. Thetranslation stage was incrementally advanced across the recordingelement by means of a lead screw turned by a microstepping motor, togive a center-to-center line distance of 10.58 μm (945 lines percentimeter or 2400 lines per inch). The laser energy impinges on therecording element in accordance with the electronic information of theimage. The energy provided by the laser drives off the image dye andother components of the dye layer at the spot where the laser beamimpinges upon the element. The removed dye and other effluents arecollected by suction. The measured total power at the focal plane was550 mW per channel maximum. A useful image was obtained.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

What is claimed is:
 1. A single sheet process of forming a dye image inthe absence of a receiving element comprising imagewise-heating, bymeans of a laser, a recording element comprising a support havingthereon a dye layer comprising an image dye dispersed in a polymericbinder, said dye layer having an infrared-absorbing material associatedtherewith, said laser exposure taking place through the side of thesupport having thereon said dye layer, and causing dye to be removedimagewise to obtain said dye image in said recording element, whereinsaid image dye is a 2-hydroxybenzophenone UV-absorbing dye.
 2. Theprocess of claim 1 wherein said UV-absorbing dye has the followingstructure: ##STR5## wherein: R¹ and R² each independently representshydroxy, alkyl, aryl, fused aryl, fused heteroaryl, carboxy,alkylcarbonyl, arylcarbonyl, hydrogen, alkenyl, cycloalkyl, haloalkyl,cyanoalkyl, hydroxyalkyl, alkoxy, alkoxyalkyl, aryloxyalkyl,alkoxyalkylcarbonyl, aryloxyalkylcarbonyl, alkoxyalkoxyalkyl,hydroxyalkoxyalkyl, tetrahydrofurfuryl, alkenyloxyalkyl,alkoxycarbonyloxyalkyl, alkenylcarbonyl, aryloxyalkylcarbonyl,aminoalkyl, cyanoalkylcarbonyl, haloalkylcarbonyl, alkylamino,arylamino, amino or halogen;m is an integer of 1 to 4; and n is aninteger of 1 to
 5. 3. The process of claim 2 wherein m and n are each 1,R¹ is CH₃, OCH₃ or C1 and R² is OH or H.
 4. The process of claim 1wherein said infrared-absorbing material is a dye which is contained insaid dye layer.